Multicellular Groups Research Articles

Vacuolar apical compartment (VAC) in breast carcinoma cell lines (MCF-7 and T47D): failure of the cell-cell regulated exocytosis mechanism of apical membrane

Abstract We have previously shown that an integral plasma membrane glycoprotein (AP2) is highly polarized to the apical domain in confluent Madin-Darby canine kidney (MDCK) epithelial cells. However, when the monolayers are prevented from forming intercellular contacts, approximately 60% of the AP2 cellular content is stored in the intracellular vacuolar apical compartment (VAC). In the current work we found that AP2 was present in the non-tumorigenic human mammary epithelial cell line MCF-10A. in the breast carcinoma cell lines MCF-7 and T47D, and in breast ductal carcinomas in vivo. By radioimmunoassay, an intracellular Compartment of AP2 was identified in the mammary cell lines in culture. In MCF-10A, this compartment behaved as in MDCK cells; namely it was observed only when the cells cannot form cell-cell contacts. However, in the carcinoma cell lines MCF-7 and T47D, a significant AP2 intracellular compartment was observed also under conditions permissive for the formation of intercellular contacts. These results were confirmed by immunofluorescence and immunoelectron microscopy experiments that showed VACs in MCF-7 and T47D, even in cells with extensive intercellular contacts. In MCF-7 cells, the addition of serum caused a partial decrease of the AP2 intracellular compartment. The exocytosis of VACs occurred towards the center of multi-cellular groups, forming intercellular lumens, similar to those transiently observed in MDCK cells and to structures described by others during embryo development. Altogether, these results suggest that VAC exocytosis is controlled by cell-cell contact signalling, which may be defective in carcinoma cells.

Vacuolar apical compartment (VAC) in breast carcinoma cell lines (MCF-7 and T47D): failure of the cell-cell regulated exocytosis mechanism of apical membrane

Abstract We have previously shown that an integral plasma membrane glycoprotein (AP2) is highly polarized to the apical domain in confluent Madin-Darby canine kidney (MDGK) epithelial cells. However, when the monolayers are prevented from forming intercellular contacts, approximately 60% of the AP2 cellular content is stored in the intracellular vacuolar apical compartment (VAC). In the current work we found that AP2 was present in the non-tumorigenic human mammary epithelial cell line MCF-10A, in the breast carcinoma cell lines MCF-7 and T47D, and in breast ductal carcinomas in vivo. By radioimmunoassay, an intracellular compartment of AP2 was identified in the mammary cell lines in culture. In MCF-10A, this compartment behaved as in MDCK cells; namely it was observed only when the cells cannot form cell-cell contacts. However, in the carcinoma cell lines MCF-7 and T47D, a significant AP2 intracellular compartment was observed also under conditions permissive for the formation of intercellular contacts. These results were confirmed by immunofluorescence and immunoelectron microscopy experiments that showed VACs in MCF-7 and T47D, even in cells with extensive intercellular contacts. In MCF-7 cells, the addition of serum caused a partial decrease of the AP2 intracellular compartment. The exocytosis of VACs occurred towards the center of multi-cellular groups, forming intercellular lumens, similar to those transiently observed in MDCK cells and to structures described by others during embryo development. Altogether, these results suggest that VAC exocytosis is controlled by cell-cell contact signalling, which may be defective in carcinoma cells.

Isolation and characterization of polyene-resistant mutants from the maize smut pathogen, Ustilago maydis, defective in ergosterol biosynthesis

Ustilago maydis mutants resistant to polyene antibiotics were screened for defects in ergosterol biosynthesis. Slow-growing mutants recovered after selecting for amphotericin B resistance were devoid of ergosterol and accumulated the methylated sterols, 14α-methylfecosterol, obtusifoliol and eburicol, indicating that these isolates were impaired in C-14 sterol demethylation and were similar to the Erg40 mutant of U. maydis. By contrast, nystatin- and pimaricin-resistant isolates which exhibited reduced growth rates showed a dysfunction in C-8 sterol isomerization. In these mutants (Erg2) ergosterol was replaced by the Δ8-sterols, ergosta-5,8,22-trienol, ergosta-8,22-dienol, fecosterol and ergost-8-enol. Analysis of a random sample of polyene-resistant isolates that grew normally revealed that although most retained a typical wild-type sterol profile, two of the isolates failed to accumulate ergosterol. The major sterols detected in these isolates were ergosta-7,22-dienol and ergosta-7-enol, suggesting a lesion in C-5 sterol desaturation in these mutants (Erg3). Of four Erg2 mutants recovered, one mutant, selected on nystatin, contained low but detectable amounts of ergosterol. Ergosterol was not detected immediately after selection in the three other pimaricin-resistant Erg2 mutants. Although the growth of three of the Erg2 mutants remained unchanged during non-selective culture, one mutant reverted and began to grow at a greater rate than the rest; analysis of the sterols produced by this strain revealed that ergosterol was now present, but at lower concentrations than those in the wild-type strain. No changes in the type of sterol formed were observed in the other slower-growing Erg2 mutants even after prolonged culture. All the Erg2 mutants exhibited morphological abnormalities; sporidia were swollen and distorted, and the inability of sporidia to separate after cell division led to the development of highly branched, multicellular groups of cells.

Escherichia coli K-12 cell-cell interactions seen by time-lapse video.

The high degree of organization in mature bacterial colonies suggests specific interactions between the cells during colony development. We have used time-lapse video microscopy to find evidence for cell-cell interactions. In its initial stages, Escherichia coli K-12 colony morphogenesis displayed control of the geometry of cell growth and involved intimate side-by-side associations. When microcolonies developed from isolated single bacteria, a directed process of elongation and division resulted in the appearance of a symmetrical four-cell array. When growth began with separate but nearby bacteria, the daughters of different cells elongated towards each other and also lined up side by side. Interactions between microcolonies containing several hundred or more bacteria were visible several hours later. Control of cell morphogenesis at later stages of microcolony development was strain specific. These results show that E. coli K-12 cells respond to each other and adjust their cellular morphogenesis to form multicellular groups as they proliferate on agar.

On the evolutionary origin of the plant mitochondrion and its genome

Higher plants occupy very different positions in the mitochondrial and nuclear lineages of global phylogenetic trees based on conserved regions of small subunit (SSU) and large subunit (LSU) rRNA sequences. In the nuclear subtree, plants branch off late, at a position reflecting a massive radiation of the major multicellular (and some unicellular) groups; in the mitochondrial subtree, in contrast, plants branch off early, near the point of connection between the mitochondrial and eubacterial lineages. Moreover, in the nuclear lineage, plants branch together with the unicellular green alga Chlamydomonas reinhardtii, whereas in the mitochondrial lineage (in both SSU and LSU trees), metaphytes and chlorophyte branch separately. Statistical evaluation indicates that the anomalous branching position of higher plants in the mitochondrial lineage is not a treeing artifact attributable to the relatively rapid rate of sequence divergence of non-plant mitochondrial rRNA sequences. In considering alternative biological explanations for these results, we are led to propose that the rRNA genes in plant mitochondria may be of more recent evolutionary origin than the rRNA genes in other mitochondria. This proposal has implications for monophyletic vs. polyphyletic scenarios of mitochondrial origin and is consistent with other evidence indicating that plant mtDNA is an evolutionary mosaic.

CELLULAR PACKETS, CELL DIVISION AND MORPHOGENESIS IN THE PRIMARY ROOT MERISTEM OF ZEA MAYS L.

Dormant meristematic cells of the unemerged radicle contained within the caryopsis of Zea mays L. are arrested in either the G1 or G2 phase of the mitotic cycle. Following germination and the resumption of root growth, each of these cells divides repeatedly to form multicellular groups, or 'packets'. The thickened cell walls that bound each packet correspond to the walls of the formerly dormant mother cell, while the thinner walls that partition the packet correspond to walls laid down when the successive rounds of division are completed. The relative thickness of these partition walls corresponds to their age, the most recently inserted wall being the thinnest. The packets thus give evidence of not only the number of divisions that have occurred since germination, but also the sequence in which these divisions took place. In addition, the elongation of the packets during root growth allows their displacement away from the root tip into the zone beyond the margin of the meristem to be measured. Using roots fixed at different times during early growth, the kinetics of packet development has been followed in cells occupying different positions within the meristem at the start of root growth. By counting the number of cells in the packets at frequent intervals during root growth, the period between each round of division has been found to be fairly constant, even as the cells are displaced towards the margin of the meristem. Variability in the interdivisional period within a packet is insufficient to cause extensive overlapping of the different rounds of division. Exceptions are found in cortical and stelar cells around the quiescent centre, where the more distal cells in a packet often divide at up to half the rate of the more proximal cells. This is evidence of a steep gradient of cell extension rate near the quiescent centre; such a gradient does not occur along packets elsewhere in the meristem. In the quiescent centre itself, cells of its cortical portion divide more rapidly than cells of its stelar portion. Cells in the cortex (but not in the stele) often divide unequally at their first transverse division; the distal (apical) daughter is usually the longer of the two daughter cells. Asymmetric, transverse division also occurs in some cells during the next rounds of division. The more rapid entry into mitosis of the longer daughter cell results in packets with particular sequences of division. Asymmetric, longitudinal (periclinal) divisions also occur in the cortex, the inner daughter cell being wider than the outer daughter cell. These periclinal divisions occur in the distal portion of the cortex near its inner and outer borders with the stele and epidermis, respectively. At the start of root growth, periclinal divisions commence sooner in the outer cortex than in the inner cortex but do not persist, and the number of cell files across the width of the cortex declines. A concurrent loss of files also occurs in the stele. The first two rounds of periclinal divisions in the innermost file of the cortex show a definite spatial pattern. These divisions intrude into the quiescent centre and may account for the apparently anomalous faster cycling cells that have been reported here. The cellular packets give insights into certain of the fundamental aspects of root morphogenesis, the choice that confronts a cell of whether to divide transversely or longitudinally being of special importance. Particular ranges of values for the ratio between cell length and breadth are associated with these two classes of division.

Structural diversity of occluding junctions in the low-resistance chloride-secreting opercular epithelium of seawater-adapted killifish (Fundulus heteroclitus).

The structural features of the chloride-secreting opercular epithelium of seawater-adapted killifish (Fundulus heteroclitus) were examined by thin-section and freeze-fracture electron microscopy, with particular emphasis on the morphological appearance of occluding junctions. This epithelium is a flat sheet consisting predominantly of groups of mitochondriarich chloride cells with their apices associated to form apical crypts. These multicellular groups are interspersed in an otherwise continuous pavement cell epithelial lining. The epithelium may be mounted in Ussing-type chambers, which allow ready access to mucosal and serosal solutions and measurement of electrocal properties. The mean short-circuit current, potential difference (mucosal-side negative), and DC resistance for 19 opercular epithelia were, respectively, 120.0 +/- 18.2 microA/cm2, 12.3 +/- 1.7 mV, and 132.5 +/- 26.4 omega cm2. Short-circuit current, a direct measure of Cl- transport, was inhibited by ouabain (5 micron) when introduced on the serosal side, but not when applied to the mucosal side alone. Autoradiographic analysis of [3H]-ouabain-binding sites demonstrated that Na+,K+-ATPase was localized exclusively to basolateral membranes of chloride cells; pavement cells were unlabeled. Occluding junctions between adjacent chloride cells were remarkably shallow (20-25 nm), consisting of two parallel and juxtaposed junctional strands. Junctional interactions between pavement cells or between pavement cells and chloride cells were considerably more elaborate, extending 0.3-0.5 micron in depth and consisting of five or more interlocking junctional strands. Chloride cells at the lateral margins of crypts make simple junctional contacts with neighboring chloride cells and extensive junctions with contiguous pavement cells. Accordingly, in this heterogeneous epithelium, only junctions between Na+,K+-ATPase-rich chloride cells are shallow. Apical crypts may serve, therefore, as focal areas of high cation conductivity across the junctional route. This view is consistent with the electrical data showing that transmural resistance across the opercular eptihelium is low, and with recent studies demonstrating that transepithelial Na+ fluxes are passive. The simplicity of these junctions parallels that described recently for secretory cells of avian salt gland (Riddle and Ernst, 1979, J. Membr. Biol., 45:21-35) and elasmobranch rectal gland (Ernst et al., 1979, J. Cell Biol., 83:(2, Pt. 2):83 a[Abstr.]) and lends morphological support to the concept that paracellular ion permeation plays a central role in ouabain-sensitive transepithelial NaCl secretion.

Argon laser microirradiation of mitochondria in rat myocardial cells in tissue culture. VII. Fibrillation in ventricle and auricle cells

Rat myocardial cells in vitro were irradiated in individual mitochondria with an argon ion laser microbeam. The contractile respone termed fibrillation in single and multicellular groups of both ventricle and auricle cells were compared. Specific correlations were made between fibrillation duration, the number of cells in the group, and the number of times the cells had fibrillated. Correlations were also made for the number of laser shots needed to induce fibrillation and the number of cells in the group. Another set of correlations were made between the pre-irradiation beat frequency and the beat frequency following recovery. Several differences and similarities of the above parameters were detected between auricle and ventricle cells. A comparison of the morphology and ultrastructure of auricle and ventricle cells also revealed significant differences.

An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian

According to modern ecological theory, high diversity at any trophic level of a community is possible only under the influence of cropping. Until herbivores evolved, single-celled algae of the Precambrain were resource-limited, and a small number of species saturated aquatic environments. In the near-absence of vacant niches, life diversified slowly. Because the changes required to produce the first algae-eating heterotrophs were therefore delayed, the entire system was self-limiting. When the "heterotroph barrier" was finally crossed in the late Precambrian, herbivorous and carnivorous protists arose almost simultaneously, for no major biological differences separate the two groups. These events automatically triggered the formation of a series of self-propagating feedback systems of diversification between adjacent trophic levels. Comparable systems arose among multi-cellular groups, which radiated rapidly from the newly diversifying protist taxa. The sudden proliferation of complex food webs formed by taxa invading previously vacant adaptive zones produced an explosive diversification of life over a period of a few tens of millions of years. The rapid appearance of skeletons in various groups, though of special geological importance, was no more dramatic than other aspects of the radiation. The overall rate of diversification was comparable to rates for less-extensive adaptive radiations of the Phanerozoic.

Argon laser micro-irradiation of mitochondria in rat myocardial cells in tissue culture: III. Irradiation of multicellular groups

Single mitochondria of contracting myocardial cells were irradiated with an argon laser microbeam and the contractility changes of the cells were noted. Four series of irradiation experiments were conducted: (i) one cell of a two-cell group was killed, (ii) one cell of a multicell group was killed, (iii) one cell of a two-cell group was damaged, (iv) one cell of a multicell group was damaged. In series (i) and (ii) a majority of cells first fibrillated and then either returned to rhythmic contraction rate, or stopped contracting. In series (iii) and (iv) the individual contractility pattern following irradiation was quite variable, but by 30 min post irradiation a majority of the cells had returned to a rhythmic contraction rate. These studies demonstrate the feasibility of using the laser microbeam to investigate cell-cell interactions, and factors involved in regulating myocardial cell contractility.

Important Aspects of Biology in National and International Economy

Research Article| November 01 1946 Important Aspects of Biology in National and International Economy H. P. K. Agersborg H. P. K. Agersborg Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1946) 9 (2): 59–60. https://doi.org/10.2307/4437773 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation H. P. K. Agersborg; Important Aspects of Biology in National and International Economy. The American Biology Teacher 1 November 1946; 9 (2): 59–60. doi: https://doi.org/10.2307/4437773 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Article PDF first page preview Close Modal You do not currently have access to this content.